This invention relates generally to fasteners and, more particularly, to pin type fasteners used with a collar to fasten a plurality of workpieces together.
Pin members of this type generally include a head and a shank formed with a plurality of ribs. The shank is inserted through aligned holes in the workpieces to be secured so that a bearing surface on the head abuts the outer surface of an outermost workpiece and so that the ribs formed on the shank extend beyond the outer surface of the other outermost workpiece. The collar, generally formed with a smooth bore, is placed over the shank and is swaged so that collar material flows into locking grooves formed between the ribs. The swaging is generally done while the shank of the pin member is held in tension. This tension is reacted at the bearing surface of the pin head as force is applied to the outer surface of the collar.
In conventional fasteners of this type, most of the axial load is carried by the rib and swaged collar material closest to the workpiece so that most failures occur there. Attempts to more evenly distribute the load among the ribs and the swaged collar material between them include the use of different rib configurations on the shank so that the locking grooves closest to the free end thereof are deeper in the radial direction than those closest to the head. See, for example, my prior U.S. Pat. No. 4,233,879; U.S. Pat. No. 3,915,053 issued to Ruhl; and U.S. Pat. No. 2,396,661 issued to Keller et al.
Because of the reduced diameter of the shank adjacent the deeper locking grooves the tensile strength of the fastener systems disclosed in the noted patents is limited. This means that the fasteners must be larger and, of course, weigh more than would be necessary if the load distribution advantages could be obtained without so reducing the diameter of the shank. The advantages obtainable from size and weight reduction make it highly desirable and, thus, an object of this invention is to provide a pin member usable with a swage collar that provides these advantages.
This problem is of even more significance where the pin member is tensioned during installation by pulling on a pintail formed as part of the shank. This pintail is connected to a locking portion, that portion formed with the ribs, by a breakneck. This breakneck is a groove formed in the shank to reduce the cross-sectional area, and, thus, the tensile strength thereof so that the pintail is broken off at a predetermined tensile load during installation. Obviously, the breakneck must be weaker than the weakest locking groove so that the breakneck fails instead of the locking groove. This causes a reduction in the installation loads that can be used and makes the use of high strength collar materials, for example, materials such as titanium or alloys of titanium and certain aluminum alloys having a strength exceeding 40% of the pin material, impractical. In order for such collar materials to flow into the locking grooves, higher installation loads are not practically achieved with reduced breakneck grooves. It is thus an object of this invention to provide a pin member usable with a collar made of high strength material.
It is yet another object of this invention to provide a pin member that provides easy flow of a high strength collar material during installation and which doesn't compromise the shear strength of the ribs or the cross-sectional area of the shank in the locking section. In contrast, merely increasing the strength of the collar material in prior art systems would shift the mode of failure in tension from shearing the collar material at the rib major diameter to shearing the pin at the rib minor diameter or failing the pin in the cross-sectional area of the shank in the locking section. In this way full advantage of the high strength collar material is realized.
It is yet another object of this invention to eliminate high bending stresses on the ribs as the collar material is swaged into the locking grooves.
Finally, it is an object of this invention to provide ribs toward the point end of the pin with sufficiently high shear strength to withstand additional loads felt by these ribs as high strength collar material is swaged into these grooves during installation.